1. Field of the Invention
This invention is in the field of blood processing and more particularly relates to the separation of blood, including whole blood, into two or more components.
2. Description of the Prior Art
Whole human blood includes at least three types of specialized cells. These are the red blood cells, white blood cells and platelets. All of these cells are suspended in plasma, a complex aqueous solution of proteins and other molecular substances.
Until relatively recently, blood transfusions have been given using whole blood. There is, however, growing acceptance within the medical profession for transfusing only those blood components required by a particular patient instead of transfusing whole blood. Transfusing only those blood components necessary preserves the available supply of blood, and in many cases, it is better for the patient. Before blood component transfusions can be widely employed, however, satisfactory blood separation techniques and apparatus must evolve.
One desirable blood separation is plasmapheresis which is the separation of whole blood into a plasma-rich component and a plasma-poor component. Typically, the plasma-rich component is retained for later use and the plasma-poor component is returned to the donor.
Presently, plasmapheresis is performed on a large scale using satellite pouch systems. A variety of satellite pouch plasmapheresis systems have been patented, and some typical examples are those systems described in U.S. Pat. No. 3,190,546 to Raccuglia et al.; U.S. Pat. No. 3,211,368 to Shanley; and U.S. Pat. No. 3,545,671 to Ross. With such systems whole blood is withdrawn from a donor and flows to a pouch containing an anti-coagulant. The pouch is then disconnected from the donor phlebotomy line, centrifuged in a swinging bucket type of centrifuge in which cells must travel about half the long dimension of the pouch, typically about 12 cm. The centrifuge must then be gently slowed to a stop and the pouch carefully lifted from the bucket of the centrifuge while avoiding remixing of the two components. The pouch is mounted in a plasma expressor and a supernatant plasma fraction is expressed into a connected plasma pouch, care being given to clamp off the connecting tube between the pouches just before plasma-poor component passes over. The pouch containing the plasma-poor component is then reconnected to the phlebotomy line so that the plasma-poor component can be returned to the donor.
It has become customary with satellite pouch systems to carry out this sequence of steps twice for each donor. Typically, one unit, or about 500 ml of whole blood is withdrawn, anti-coagulated and separated. Approximately 250 ml of plasma-rich component is obtained and the plasma-poor component is returned to the donor. Subsequently, another unit of whole blood is withdrawn and processed in a similar manner. Using such techniques with satellite pouch systems, it often takes approximately 11/2 hours to obtain 500 ml of separated plasma-rich component and to return the plasma-poor component to the donor, even though the time for donating a unit of whole blood is only about 20 minutes. This relatively long processing time imposes a major limitation on volunteer donor recruitment. Additionally, because the blood pouch is disconnected from the donor at the end of each withdraw cycle and transported to and from a separate centrifuge room for centrifugation, there is always the danger of returning blood components to a donor which are not his own. Satellite pouch systems require particularly careful handling of the pouch containing separated plasma-rich and plasma-poor components to avoid remixing thereby ruining the separation.
Blood cell separation systems, both continuous and intermittent flow, have been placed in widespread use but have not been accepted for widespread application in plasmapheresis because the disposable blood pathways used are too expensive relative to the satellite pouch systems. An example of a recently developed plasmapheresis apparatus is described by Latham in U.S. Pat. No. 4,086,924. In this apparatus, whole blood can be withdrawn from a donor using a phlebotomy needle and pressure cuff. The whole blood is anti-coagulated and transported by a blood pump to a plasmapheresis centrifuge where it is separated into plasma-rich and plasma-poor components. Separated plasma-rich component is stored in a plasma container. When a predetermined quantity of separated plasma-rich component has been obtained, cycle control means immediately switch from the withdraw cycle to a return cycle. The cycle control means also immediately switch from the return cycle to either a withdraw cycle or a standby cycle in response to a signal from monitoring means indicating that the return of plasma-poor component has been completed. The manufacturing costs of the disposable blood pathway for this system has been greater than that for a satellite pouch system, however, and although the Latham system is attractive because of the short (30 min.) donor time required, it has involved too much expense to be accepted for use on a wide scale.
One main reason for the relatively high expense of the disposable blood pathway in prior blood separation systems of the Latham type relates to the requirement for a specially manufactured blood centrifuge bowl. Many times, for example, parts for these are injection molded from relatively expensive materials, such as polycarbonate, which adds a major element of expense to the disposable blood pathway. Another reason for the relatively high expense in the Latham system is the requirement for precisely manufactured rotary seals to pass blood in and plasma-rich component out of the centrifuge bowl as it is spinning. It is theoretically possible to eliminate such inordinate expense, therefore, by employing a relatively inexpensive, disposable blood bag as the processing chamber and by eliminating the requirement for a rotary seal. Blood separation systems have been designed with one or both of these in mind, but such systems have invariably suffered from their own set of problems and disadvantages.
Mitchell et al., in U.S. Pat. No. 3,674,197, for example, point out some problems encountered with attempts to use standard flexible blood bags in a centrifuge rotor. The problems mentioned relate to the necessity to properly support the liquid filled bags because they are subjected to various pressures and forces during centrifugation which are not evenly distributed. The shifting of position of the flexible blood bags causes wrinkles and folds in the bag material with consequent imbalancing of the rotor. The Mitchell et al. invention disclosed in this patent relates to contoured shoes which surround a cylindrical flexible blood processing bag to alleviate such problems. However, there is no attempt by these patentees to provide a contoured blood processing chamber which supports a standard blood bag in a position to achieve centrifugal separation by minimizing the distance that the blood components are required to travel during centrifugation.
Another approach to using a flexible blood processing bag in a centrifugation system is disclosed by Jones et al. in U.S. Pat. No. 3,737,096. The highly specialized system disclosed therein is a cell washing system in which a flexible blood bag receives fluid and has fluid withdrawn from it during operation of the centrifuge. The volume of the processing chamber in this centrifuge is adjusted by a flexible membrane connected to a displacement fluid which expands or contracts, respectively, in reponse to introduction of or withdrawal of a displacement fluid. This system has the disadvantage of requiring a rotary seal. Additionally, the flexible bag is relatively complex and does not have a design intended to minimize the distance which blood components travel during separation.
As can be appreciated from the above discussion, there has been very considerable effort applied to developing new blood processing systems. Despite this, none of the systems developed heretofore provide the combination of inexpensive disposable blood processing sets, rapid separation, ease of making a fine cut between different blood components and the capability to carry out the entire blood processing immediately adjacent to a blood donor.